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Peptide Nomenclature Guide

Symbols and structures for amino acids

Common (“proteinogenic” or “coded”) amino acids have a three-letter symbol and are also represented by a one-letter symbol. Uncommon amino acids also have three-letter symbols and can be represented by the one-letter symbol “X”. The tables below list the symbols and abbreviations used in our website and literature.

Table 1. Common Amino Acids Table 2. Uncommon Amino Acids Table 3. Substituents

Table 1. Common Amino Acids

Key -  Acidic    Basic    Non-polar (hydrophobic)    Polar (uncharged)

Amino acid Three-letter symbol One-letter symbol Chemical structure
Alanine Ala A Alanine
Arginine Arg R Arginine
Asparagine Asn N Asparagine
Aspartic acid Asp D Aspartic acid
Cysteine Cys C Cysteine
Glutamine Gln Q Glutamine
Glutamic acid Glu E Glutamic acid
Glycine Gly G Glycine
Histidine His H Histidine
Isoleucine Ile I Isoleucine
Leucine Leu L Leucine
Lysine Lys K Lysine
Methionine Met M Methionine
Phenylalanine Phe F Phenylalanine
Proline Pro P Proline
Serine Ser S Serine
Threonine Thr T Threonine
Tryptophan Trp W Tryptophan
Tyrosine Tyr Y Tyrosine
Valine Val V Valine

Table 2. Uncommon Amino Acids

Three letter symbol Amino Acid
Aad 2-Aminoadipic acid (2-aminohexanedioic acid)
Aan α-Asparagine
Abu 2-Aminobutanoic acid
Aca 2-Aminocapric acid (2-aminodecanoic acid)
Agn α-Glutamine
Ahx 6-Aminohexanoic acid
Aib α-Aminoisobutyric acid (α-methylalanine)
Apm 2-Aminopimelic acid (2-aminoheptanedioic acid)
App γ-Amino-β-hydroxybenzenepentanoic acid
Asu 2-Aminosuberic acid (2-aminooctanedioic acid)
AzaGly 2-Azaglycine
Aze 2-Carboxyazetidine
Bal β-Alanine
Bas β-Aspartic acid
Bly 3,6-Diaminohexanoic acid (β-lysine)
Bua Butanoic acid
Bux 4-Amino-3-hydroxybutanoic acid
Cap γ-Amino-β-hydroxycyclohexanepentanoic acid
Cha 3-Cyclohexylalanine
Cit N5-Aminocarbonylornithine
Cya 3-Sulfoalanine
Dab 2,4-Diaminobutanoic acid
Dap Diaminopropionic acid
Dpm Diaminopimelic acid
Dpr 2,3-Diaminopropanoic acid
Dsu 2,7-Diaminosuberic acid (2,7-diaminooctanedioic acid)
Edc S-Ethylthiocysteine
Ggu γ-Glutamic acid
Gla γ-Carboxyglutamic acid
Glc Hydroxyacetic acid (glycolic acid)
Glp Pyroglutamic acid (Pyr) (pGlu)
Har Homoarginine
Hcy Homocysteine
Hhs Homohistidine
Hiv 2-Hydroxyisovaleric acid
Hse Homoserine
Hva 2-Hydroxypentanoic acid
Hyl 5-Hydroxylysine
Hyp 4-Hydroxyproline
Igl α-Amino-2-indanacetic acid
Iva Isovaline
Lac 2-Hydroxypropanoic acid (lactic acid)
Maa Mercaptoacetic acid
Mba Mercaptobutanoic acid
Mhp 3-Hydroxy-4-methylproline
Mpa Mercaptopropanoic acid
Nal 3-Naphthylalanine
Nle Norleucine
Nphe N-Benzylglycine
Nty Nortyrosine
Nva Norvaline
Oaa ω-Amino acid
Oic 2-Carboxyoctahydroindole
Orn Ornithine
3-Pal 3-(3-Pyridyl)-alanine
Pen Penicillamine (3-mercaptovaline)
Phg 2-Phenylglycine
Pip 2-Carboxypiperidine
Pmp β,β-Cyclopentamethylene-β-Mercaptopropionic acid
pSer Phospho-L-serine
pThr Phospho-L-threonine
pTyr Phospho-L-tyrosine
Pya(4) 3-(4-Pyridinyl)-alanine
Sar Sarcosine (N-methylglycine)
Spg 1-Amino-1-carboxycyclopentane
Sta Statine ((3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid) (AHMHA) 
Thi 3-Thienylalanine
Tac 2-Tolylaminophenylcabonyl ([(2-Methylphenyl)amino]carbonyl)
Tic 3-Carboxyisoquinoline
Tle 3-Methylvaline
Tml ε-N-Trimethyllysine
Tza 3-Thiazolylalanine
Und Undefined
Wil α-Amino-2,4-dioxopyrimidinepropanoic acid

Table 3. Substituents

Abbreviation Substituent
Ac Acetyl
Bn Benzyl, Bzl
Bz Benzoyl
For Formyl
Me Methyl
Myr Myristoyl
Z Benzyloxycarbonyl